Packet processors are used in network devices to handle the routing of packets. Packet processors are typically implemented as RISC (Reduced Instruction Set Computers) processor. In some instances these packet processors are implemented as programmable/multithreaded devices. The key benefits of multi-threaded packet processors include simpler instruction execution pipeline eliminating pipeline hazards, resource conflicts, branch delays, pipeline stalls, and pipeline stage bypasses. Another advantage of these type of processors is they provide a simpler programming model by hiding memory access latencies, hiding coprocessor latencies, eliminating branch delays, removing operand dependencies, provide better utilization of available memory bandwidth and better utilization of coprocessors.
Content-addressable Memory (CAM) is often used in computer networking devices. For example, when a network switch receives a data frame from one of its ports, it updates an internal table with the frame's source MAC address and the port it was received on. It then looks up the destination MAC address in the table to determine what port the frame needs to be forwarded to, and sends it out on that port. The MAC address table is usually implemented with a binary CAM so the destination port can be found very quickly, reducing the switch's latency.
Ternary CAMs are often used in network routers, where each address has two parts: the network address, which can vary in size depending on the subnet configuration, and the host address, which occupies the remaining bits. Each subnet has a network mask that specifies which bits of the address are the network address and which bits are the host address. Routing is done by consulting a routing table maintained by the router which contains each known destination network address, the associated network mask, and the information needed to route packets to that destination. Without CAM, the router compares the destination address of the packet to be routed with each entry in the routing table, performing a logical AND with the network mask and comparing it with the network address. If they are equal, the corresponding routing information is used to forward the packet. Using a ternary CAM for the routing table makes the lookup process very efficient. The addresses are stored using “don't care” for the host part of the address, so looking up the destination address in the CAM immediately retrieves the correct routing entry; both the masking and comparison are done by the CAM hardware.